In a typical magnetic storage system, digital data is stored in a series of concentric circles or spiral tracks along a storage medium. Data is written to the medium by positioning a read/write head assembly over the medium at a selected location as the storage medium is rotated, and subsequently passing a modulated electric current through the head assembly such that a corresponding magnetic flux pattern is induced in the storage medium. To retrieve the stored data, the head assembly is positioned anew over the track as the storage medium is rotated. In this position, the previously stored magnetic flux pattern induces a current in the head assembly that can be converted to the previously recorded digital data.
A servo control system is used to move the read/write head assembly across the storage medium as the medium is rotated, and may also control the rotation speed and therefore the frequency at which servo data is read. The read/write head assembly must be positioned correctly by the servo control system to properly read stored data. Patterns stored in servo regions or servo wedges on the storage medium enable the servo control system to position the read/write head assembly. In some servo control systems, a Hamming detector is used to detect a servo address mark in the servo data. However, Hamming detectors have limited performance, particularly in asynchronous sampling detection systems.